Photoelectrophoretic imaging process employing a finely divided phthalocyanine pigment

ABSTRACT

Phthalocyanine pigments are used as electrically photosensitive particles in a photoelectrophoretic imaging system.

United States Patent Leonard M. Carreira Webster;

Vsevolod Tulagin, Rochester, both of N.Y. 560,603

June 27, 1966 Oct. 26, 1971 Xerox Corporation Rochester, N.Y.

Continuation-impart of application Ser. No. 384,737, July 23, 1964, nowPatent No. 3,384,565

Inventors Appl. No. Filed Patented Assignee PHOTOELECTROPHORETIC IMAGINGPROCESS EMPLOYING A FINELY DIVIDED PHTHALOCYANINE PIGMENT 10 Claims, 1Drawing Fig.

US. Cl 96/88, 96/1 R, 96/1.2,96/1.3, 204/181, 260/314.5

[51] Int. Cl G030 7/00, BOlk 5/00 [50] Field of Search 96/1, 1.5,

References Cited Primary Examiner-Charles E. Van Horn Attorneys-StanleyZ. Cole and James J. Ralabate ABSTRACT: Phthalocyanine pigments are usedas e1ectrica11y photosensitive particles in a photoelectrophoreticimaging system.

PATENTE-DHET 261911 3,615,558

INVENTORS. VSEVOLOD TULAGIN EONARD M. CARREIRA BY z Kb .Qwm

A TTORNE Y5 PHOTOELECTROPHORETIC IMAGING PROCESS This application is acontinuation-in-part of application Ser. No. 384,737 filed July 23, 1964now U.S. Pat. No. 3,384,565 issued May 21, 1968. I

This invention relates in general to imaging methods. More specifically,the invention concerns the use of electrically photosensitive pigmentsin electrophoretic imaging systems.

There has been recently developed an electrophoretic imaging systemcapable of producing color images which utilizes photosensitiveparticles. This process is described in detail and claimed in copendingapplications now U.S. Pat. No. 3,384,56; 384,681 abandoned in favor ofcontinuing application Ser. No. 655, 03 now U.S. Pat. No. 3,384,566 andA EILPHHALQQXA E.

384,680 abandoned in favor of continuing application Ser.

No. 518,041 now U.S. Pat. No. 3,383,993. In such an imaging system,various colored light absorbing particles are suspended in anonconductive liquid carrier. The suspension placed between electrodes,subjected to a potential difference and exposed to an image. As thesesteps are completed, selective particle migration takes place in imageconfiguration, providing a visible image at one or both of theelectrodes. An essential component of the system is the suspendedparticles which must be intensely colored and electricallyphotosensitive and which apparently undergo a net change in chargepolarity upon exposure to activating radiation, through interaction withone of the electrodes. The images are produced in color because mixturesof two or more differently colored sets of particles which are eachsensitive only to light of a specific wavelength or narrow range ofwavelengths are used. Particles used in this system must have bothintense pure colors and be highly photosensitive. The pigments of theprior art often lackthe purity and brilliance of color, the high degreeof photosensitivity, and/or periodic table. Also, it is well known thatfrom 1 to 16 of the peripheral hydrogen atoms on the 4 benzene rings ofthe phthalocyanine molecule may be replaced by halogen atoms andnumerous organic and inorganic groups.

Phthalocyanine is known to exist in several different 3 polymorphicforms which may be easily distinguished by comparison of their X-raydiffraction patterns and/or infrared spectra. Also, the color of thepigment varies according to the polymorphic form, the beta form being,in general, greener that the alpha or gamma forms. The alpha, beta andgamma forms of phthalocyanine are described by C. Hammon and M. Starke,inlnvestigation of the Electrical and Thermal-Electric properties of theModification of Metal-Free Phthalocyanine," Phys. state Vol. 4, 509(1964).A recently discovered polymorphic form of metal-freephthalocyanine, termed the xform, is described in copending applicationSer. No. 505,723, now U.S. Pat. No. 3,357,989 filed Oct. 29, 1965.Several additional polymorphs of metal containing phthalocyanine areknown, i.e., R0 -fonn, disclosed in U.S. Pat. No. 3,051,721; delta formdescribed in U.S. Pat. No. 3,160,635 and another delta" form describedin U.S. Pat. No. 3,150,150.

Several different forms of phthalocyanine polymers are known, Several ofthese phthalocyanine containing polymers are described on pages 328-337of Phthalocyanine Compounds" by F. H. Moser and A.L. Thomas, RheinholdPublishing Corporation, New York, 1963).

the preferred correlation between the peak spectral response and peakphotosensitivity necessary for use in such a system.

it is therefore an object of this invention to provide elecin additionto the unsubstituted phthalocyanine of the above structure, variousmetal derivatives of phthalocyanine are known in which the two hydrogenatoms in the center of the molecule are replaced by metals from anygroup of the Of the compositions within the general formula listedabove, the unsubstituted, metal-free phthalocyanines in the alpha and xpolymorphic forms are preferred for use in an electrophoretic imagingprocess since they have the highest photosensitivity and most desirablecolor. The x" crystal form is especially preferred for use inmonochromatic imaging since it has substantially panchromatic spectralresponse. 0n the other hand, the appha-form, or mixtures of thealpha-form with other forms, is preferred for use in ploychromaticimaging since it has the most desirable color and most appropriatespectral response for use in subtractive polychromatic imagmg.

Since the shade or tone of the phthalocyanine and the spectral andphotosensitive response varies depending upon the crystal form and thesubstituents, intermediate values of these variables may be obtained bymixing several of the different phthalocyanines. Any suitablephthalocyanine may be used in the electrophoretic imaging processes ofthis invention. Typical phthalocyanines including unsubstitutedmetal-free phthalocyanine, aluminum phthalocyanine, aluminum polychlorophthalocyanine, antimony phthalocyanine, barium phthalocyanine,beryllium phthalocyanine, cadmium hexadecachlorophthalocyanine, cadmiumphthalocyanine, calcium phthalocyanine, cerium phthalocyanine, chromiumphthalocyanine, cobalt phthalocyanine, cobalt chlorophthalocyaninecopper 4-aminophthalocyanine, copper bromochlorophthalocyanine, copper4-chlorophthalocyanine, copper 4-nitrophthalocyanine, copperphthalocyanine, copper phthalocyanine sulfonate, copperpolychlorophthalocyanine, deuteriophthalocyanine, dysprosiumphthalocyanine, erbium phthalocyanine europium phthalocyanine,gadolinium phthalocyanine, gallium phthalocyanine, germaniumphthalocyanine, hafnium phthalocyanine, halogen substitutedphthalocyanine, holmium phthalocyanine, indium phthalocyanine, ironphthalocyanine, phthalocyanine, iron polyhalophthalocyanine, lanthanumphthalocyanine, lead phthalocyanine, lead polychlorophthalocyanine,cobalt hexaphenylphthalocyanine, copper pentaphenylphthalocyanine,lithium phthalocyanine, lutecium phthalocyanine, magnesiumphthalocyanine, manganese phthalocyanine, mercury phthalocyanine,molybdenum phthalocyanine, napthalocyanine, neodymium phthalocyanine,nickel phthalocyanine, nickel polyhalophthalocyanine, osmiumphthalocyanine, palladium phthalocyanine, palladiumchlorophthalocyanine, al- -koxyphthalocyanine, alkylaminophthalocyanine,alkylmer- 'captophthalocyanine, aralkylaminophthalocyanine,aryloxyphthalocyanine, arylemercaptophthalocyanine copper phthalocyaninepiperidine, cycloalkylaminophthalocyanine, dialkylaminophthalocyanine,diaralkylaminophthalocyanine, dicycloalkylaminophthalocyanine,hexadecahydrophthalocyanine, imidomethlylphthalocyanine, 1,2naphthalocyanine, 2,3, naphthalocyanine,octaazaphthalocyanine, sulfurphthalocyanine, tetraazaphthalocyanine,tetra-4-acetylaminophthalocyanine, tetra-4-aminobenzoylphtalocyanine,tetra-4- aminophthalocyanine, tetrachloromethylphthalocyanine,tetradiazophthalocyanine, tetra-4,4 dimethyloctaazapthalocyanine,tetra-4,S-diphenylene-dioxide phthalocyanine, tetra-4,5-diphenyloctaazaphthalocyanine, tetra-( 6-methylbenzothiazoyl)phthalocyanine, tetra-p-methylphenylaminophthalocyanine,tetra-methylphthalocyanine, tetranaphthotriazolphthalocyanine,tetra-4-naphthalocyanine, tetra-4-nitrophthalocyanine,tetra-peri-naphthylene-4,5-octatazaphthalocyanine,tetra-2,3-phenylenexoide phthalocyanine,tetra-4-phenyloctaazaphthalocyanine, tetraphenylphthalocyanine,tetraphenylphthalocyanine tetracarboxylic acid,tetraphenylphthalocyanine tetrabarium carboxylate,tetraphenylphthalocyanine tetra-calcium carboxylate,tetrapyridyphathalocyanine,tetra-4-trifluoro-methylmercaptophthalocyanine,tetra-4-trifluoromethylphthalocyanine, 4,5-thinonaphthene-octaazaphthalocyanine, platinum phthalocyanine, potassiumphthalocyanine, rhodium phthalocyanine, samarium phthalocyanine, silverphthalocyanine, silicone phthalocyanine, sodium phthalocyanine,sulfonated phthalocyanine, thorium phthalocyanine, thuliumphthalocyanine, tin chlorophthalocyanine, tin phthalocyanine, titaniumphthalocyanine, uranium phthalocyanine, vanadium phthalocyanine,ytterbium phthalocyanine, zinc chlorophthalocyanine, zincphthalocyanine, Together with, or in lieu of, the above phthalocyanines,any suitable mixture, dimer, trimer, oligomer, polymer, copolymer ormixtures of phthalocyanines may be used, The phthalocyanine may also bein any suitable crystal form. I

The use of the above compositions and electrophoretic imaging will bebetter understood upon reference to the draw ing which showsschematically and exemplary electrophoretic imaging system.

Referring now to the figure,.t here is seen a transparent electrodegenerally designated 1 which, in this exemplary instance, is made up ofa layer of optically transparent glass 2 overcoated with a thinoptically transparent layer 3 of tin oxide, commercially available underthe name NESA glass. This electrode will hereafter be referred to as theinjecting electrode." Coated on the surface of injecting electrode 1 isa thin layer 4 of finely divided photosensitive particles dispersed inan insulating liquid carrier. The term photosensitive," for the purposesof this application, refers to the properties of a particular which,once attracted to the injecting electrode, will migrate away from itunder the influence of an applied electric field when it is exposed toactinic electromagnet radiation. For a detailed theoretical explanationof the apparent mechanism of operation of the invention, see theabove-mentioned copending applications Ser. Nos. 384,737; 384.361 and384,680, the disclosures of which are incorporated herein by reference.Liquid suspension 4 may also contain a sensitizer and/or a binder forthe pigment particles which is at least partially soluble in thesuspending or carrier liquid as will be explained in greater detailbelow. Adjacent to the liquid suspension 4 is a second electrode 5,hereinafter called the blocking electrode," which is connected to oneside of the potential source 6 through a switch 7. The opposite side ofthe potential source 6 is connected to the injecting electrode 1 so thatwhen switch 7 is closed, an electric field is applied across the liquidsuspension 4 between electrodes 1 and 5. An image projector made up of alight source 8, a transparency 9, and a lens 10 is provided to exposethe dispersion 4 to a light image of the original transparency 9 to bereproduced. Electrode 5 is made in the form of a roller having aconductive central core 11 connected to the potential source 6. The coreis covered with a layer of a blocking electrode material 12, which. maybe I Baryta paper. The pigment suspension is exposed to the image to bereproduced while a potential is applied across the blocking andinjecting electrodes by closing switch 7. Roller 5 is caused to rollacross the top surface of injecting electrode 1 withswitch 7 closedduring the period of image exposure. This light exposure causes exposedpigment particles originally attracted to electrode 1 to migrate throughthe liquid and adhere to the surface of the blocking electrode, leavingbehind a pigment image on the injecting electrode surface which is aduplicate of the original transparency 9. After exposure, the relativelyvolatile carrier liquid evaporates off, leaving behind the pigmentimage. This pigment image may then be fixed in place as, for example, byplacing a lamination over its top surface or by virtue of a dissolvedbinder material in the carrier liquid such as parafiin wax or othersuitable binder that comes out of solution as the carrier liquidevaporates. About 3 percent to 6 percent by weight of parafiin binder inthe carrier has been found to produce good results. The carrier liquiditself may be paraffin wax or other suitable binder. In the alternative,the pigment image remaining on the injecting electrode may betransferred to another surface and fixed thereon. As explained ingreater detail below, this system can produce either monochromatic orpolychromatic images depending upon the type and number of pigmentssuspended in the carrier liquid and the color of light to which thissuspension is exposed in the process.

Any suitable insulating liquid may be used as the carrier for thepigment particles in the system. Typical carrier liquids are decane,dodecane, N-tetradecane, paraffin, beeswax or other thermoplasticmaterials, Sohio Odorless Solvent 3440, (a kerosene fraction availablefrom Standard Oil Company of Ohio and lsopar-G, (a long chain saturatedaliphatic hydrocarbon available from Humble Oil Company of New Jersey).Good quality images have been produced with voltages ranging from 300 to500 volts in the apparatus of the figure.

In a monochromatic system, particles of a single composition aredispersed in the carrier liquid and exposed to a blackand-white image. Asingle color image results, corresponding to conventionalblack-and-white photography. in a polychromatic system, the particlesare selected so that those of different colors respond to differentwavelengths in the visible spectrum corresponding to their principalabsorption bands. Also, the pigments should be selected so that theirspectral response curves do not have substantial overlap, thus allowingfor color separation and subtractive multicolor image formation. In atypical multicolor system, the particle dispersion should include cyancolored particles sensitive mainly to red light, magenta particlessensitive mainly to green light and yellow colored particles sensitivemainly to blue light. When mixed together in a carrier liquid, theseparticles produce a black appearing liquid. When one or more of theparticles are caused to migrate from base electrode 1 toward an upperelectrode, they leave behind particles which produce a color equivalentto the color of the impinging light. Thus, for example, red lightexposure causes the cyan colored pigment to migrate, leaving behind themagneta and yellow pigments which combine to produce red in the finalimage. In the same manner, blue and green colors are reproduced byremoval of yellow and magenta, respectively. When white light impingesupon the mix, all pigments migrate, leaving behind the color of thewhite or transparent substrate. No exposure leaves behind all pigmentswhich combine to produce a black image. This is an ideal technique ofsubtractive color imaging in that the particles are not only eachcomposed of a single component but, in addition, they perform the dualfunctions of final image colorant and photosensitive medium.

It has been found that the compounds of the general formula given aboveare surprisingly effective when used in either a single or multicolorelectrophoretic imaging system. Their good spectral response and highphotosensitivity result in dense, brilliant images. The pigments hereindisclosed have suprisingly good color separation and image densitycharacteristics.

Any suitable different colored photosensitive pigment particles havingthe desired spectral responses may be used with the pigments of thisinvention to fon'n a pigment mix in a carrier liquid for color imaging,From about 2 to about percent pigment by weight have been found toproduce good results. The addition of small amounts (generally rangingfrom 0.5 to 5 percent) of electron donors or acceptors to thesuspensions may impart significant increases in system photosensitivity.

The following examples further specifically define the present inventionwith respect to the use of the compositions of the general formula givenabove in electrophoretic imaging processes. Parts a percentages are byweight unless otherwise indicated. The examples below are intended toillustrate various preferred embodiments of the electrophoretic imagingprocess of the present invention.

All of the following examples are carried out in an ap paratus of thegeneral type illustrated in the figure with the imaging mix 4 coated ona NESA glass substrate through which exposure is made. The NESA glasssurfaced is connected in series with a switch, a potential source, andthe conductive center of a roller having a coating of Baryta paper onits surface. The roller is approximately 2%inches in diameter and ismoved across the plate surface at about 4 cm. per second. The plateemployed is roughly 4 inches square and is exposed with a lightintensity of about 4,000 ft./candles as measured on the uncoated NESAglass surface. Unless otherwise indicated, 8 percent by weight of theindicated pigment and each example is suspended in Sohio OdorlessSolvent 3440. All pigments which have a relatively large particle sizeas received commercially or as synthesized are ground in a ball mill forabout 48 hours to produce their size to provide a more stable dispersionwhich improves resolution of the final image. In examples I -X, theexposure is made with a 3,200 K. lamp through a 0.30 neutral densitystep wedge filter to measure the sensitivity of the suspensions to whitelight and then Wratten filters 29, 61 and 47 b are individuallysuperimposed over the light source in separate tests to measure thesensitivity of the suspensions to red, green and blue lightrespectively.

EXAMPLE] About eight parts of Monarch Green Toner, a polychloro copperphthalocyanine, C. I. No. 74,260, available from Imperial Color andChemical Company, is suspended in about 100 parts of Sohio OdorlessSolvent 3440 The mixtures coated on the NESA glass substrate and apositive potential of about 2,500 volts is imposed on the rollerelectrode. The plate is exposed in separate runs to white, red, greenand blue light as described above. The results are tabulated in table I,below. As can be seen from the table, this pigment is sensitive to redlight.

EXAMPLE ll About eight parts of Cyan Blue GTNF, the beta form of copperphthalocyanine, C. I. No. 74160, available from American Cyanamide issuspended in about 100 parts of Sohio Odorless Solvent 3440. The mixtureis coated on a N ESA glass substrate and the plate is exposed as inexample 1. Here, the potential imposed is +2.500 volts. Sensitivity isindicated in table 1.

EXAMPLE "I About eight parts of Cyan Blue BNF, the alpha form of copperphthalocyanine, C. I. No. 74160, available from American Cyanamide issuspended in about 100 parts of Sohio Odorless Solvent 3440. The mixtureis exposed to a stepwedge filter through a color filter while a positivepotential of about 2,500 volts is imposed on the roller electrode. Asindicated in table 1, this pigment has fairly low sensitivity.

About eight parts of Cyan Blue XR, the alpha form of copperphthalocyanine, available from American Cyanamide is suspended in about100 parts Sohio Odorless Solvent 3440. This mixture is coated onto fourNESA glass substrates, each of which is exposed through a neutraldensity step-wedge filter and a color filter as described above. In eachcase, the potential applied is 2,500 volts. As indicated in table I,this pigment has good sensititvity, primarily to red light.

EXAMPLE V About eight parts of Monarch Blue G, copper phthalocyanine,available from Imperial Color and Chemical Company, is suspended inabout parts Sohio odorless Solvent 3440. The mixture is coated onseveral NESA glass substrates and exposure in this instance is 2,500volts. As shown by table I, this pigment has high sensitivity.

EXAMPLE VI About eight parts of the beta form of metal-freephthalocyanine is suspended in about 100 parts of Sohio Odorless solvent3440. This pigment is prepared by milling Monolite Fast Blue GS, thealpha form of metal-free phthalocyanine, C. I. No. 74100, available fromthe Arnold Hofiman Company, in o-dichlorobenzene. The suspension iscoated onto N ESA glass substrate and imaging tests are performed asdescribed above. A positive potential of about 2,500 volts is maintainedon the roller electrode during exposure. A second set of tests is thenrun with a negative potential. As is indicated in table I, this pigmenthas high sensitivity.

EXAMPLE Vll About eight parts of Monolite Fast Blue GS, the alpha formof metal-free phthalocyanine, C. I. No. 74100, available from the ArnoldHoffman Company is suspended in about lOO parts of Sohio OdorlessSolvent 3400. The mixture is coated onto NESA glass substrates andimaged as described above. A positive potential of about 2,500 volts ismaintained on the roller electrode during imaging. A second set of testsis run with a negative potential. As indicated in table I, this pigmenthas high sensitivity.

About eight parts of Non-Floc Green Shade Phthalocyanine Blue Lake,benzoated copper phthalocyanine, available from Harmon colors, issuspended in about 100 parts of Sohio Odorless Solvent 3440. Thesuspension is coated on several NESA glass substrates and images areproduced as described above. A positive potential of about 2,500 voltsis maintained on the roller electrode during imaging. As'indicated intable I, this pigment has good sensitivity, responding only to redlight.

EXAMPLE lX A sample of commercial Monolite Fast Blue GS is heated in anoxygen atmosphere at about 320 C. for about Ix hours. This appears togive the beta form of metal-free phthalocyanine. About eight parts ofthis pigment is suspended in about 100 parts of Sohio Odorless Solvent3400. The suspension is coated onto a plurality of NESA glasssubstrates. A set of imaging tests as described above is performed withthe roller electrode held at a positive potential of about 2,500 volts.A second set of imaging tests in then performed with the rollerelectrode at a negative potential of about 2,500 volts. As indicated intable l, the positive roller potential gives higher sensitivity.

EXAMPLE X About eight parts of the x form of phthalocyanine, prepared asdescribed in copending application Ser. No. 505,723, filed Oct. 29,i965, is suspended in about 100 parts of Sohio Odorless Solvent 3400.Two sets of Nesa glass substrates are coated with the suspension. Thefirst is imaged as described above, while the roller electrode is heldat a positive potential of about 2,500 volts. The second set is imagedwhile the roller electrode is held at a negative potential of about2,500 volts. As indicated in table I, this form of phthalocyanine has asubstantially panchromatic response.

The electrophoretic sensitivity of the pigments to red,

green, blue, and white light is tested according to conventionalphotographic methods and the results are recorded in table I above. Inthe table, the first column lists the number of the test example. Thesecond column gives the positive or negative electrical potentialapplied to the roller electrode in volts. The third through sixthcolumns give the photographic speed of the various suspensions to blue,green, red and white light respectively in camera stops. The sensitivityis a measure of the exposure necessary to produce a visible image on theNESA surface as determined by the number of step-wedge filter steps ofmigrated pigment visible on the NESA. Thus, for example, in example I,red light will produce an image at a250f.c. exposure while white lightwill produce an image at 125 f.c. exposure. As shown by the above table,the tested pigments are primarily sensitive to red light. As discussedabove, for polychromatic imaging, it is preferred that cyan pigments beresponsive only to red light. On the other hand, as shown by example X,some forms of phthalocyanine are substantially sensitive to all colorsof light and would be preferred for use in a monochromatic system.

in each of examples XI-XV below, a suspension including equal amounts ofthree different pigments is made up by dispersing the pigments in finelydivided form in Sohio Odorless Solvent 3400 so that the pigmentsconstitute about 8 percent by weight of the mixture. This mixture may bereferred to as a trimix. The mixtures are individually tested by coatingthem on a NESA glass substrate and exposing them as in example I above,except that a multicolor Kodachrome transparency is interposed betweenthe light source and the NESA plate instead of the neutral density andWratten filters. Thus, a multicolored image is projected on thesuspension as the roller moves across the surface of the coated NESAglass substrate. A Baryta paper blocking electrode is employed and theroller is held at a negative potential of about 2,500 volts with respectto the substrate. The roller is passed over the substrate six times. Theroller is cleaned after each pass. The potential application andexposure are both continued during the entire period of the six passesby the roller.

EXAMPLE XI The pigment suspension consists of a magenta pigment,Watchung Red B, the barium salt of l-(4'-methyl-5'-chloroazobenzene-2-sulfonic acid)-2-hydroxy-3-naphthoic acid, C. I. No.15865, available from E. I. duPont de Nemours & Company; a yellowpigment, Algol yellow GC, C. I. No. 67300,l,2,5,6-di(C,C'-diphenyl)-thiazole-anthraquinone available form GeneralDyestuffs; and as a cyan pigment, Monolite Fast Blue GS, the alpha formof metal-free phthalocyanine, C. I. No. 74100, available from the ArnoldHoffman Company, This trimix, when exposed to a multicolor image asdescribed above, produces a full color image with good density andexcellent color separation.

EXAMPLE XII The pigment suspension consists of a magenta pigment,Bonadur Red B. l-(4'-ethyl-5-chloroazobenzene-2'-sulfonic acid)-2-hydroxy- 3 -naphthoic acid calcium lake, available fromAmericanCyanamide; a yellow pigment, N-2"-pyridyl- 8,13-dioxadinaphtholfuran-6-carboxamide, prepared as described in copending application, Ser. No.421,281, filed Dec. 28, 1964 and as a cyan pigment, Cyan Blue XR, thealpha form of copper phthalocyanine, C. I. No. 74160, available fromAmerican Cyanamide. This trimix is exposed to a multicolor image andproduces a full color image of good density and color separation.

EXAMPLE XIII A pigment suspension is prepared consisting of a magentapigment, Naphthol Red B, l-(2'-methoxy5.'-nitrophenylazo)-2-hydroxy-3'-nitro-3-naphthanilide, C. I. No. 12355, available fromCollway Colors; a yellow pigment, l-cyano-2,3-(3'- nitrol-phthaloyl-7,benzopyrrocoline prepared as described in copending application Ser. No.445,235, Apr. 2, 1965; and as a cyan pigment, Cyan Blue GTNF, the betaform of copper phthalocyanine, available from Collway Colors. Thistrimix is exposed to a multicolor image and produces a full color imageof satisfactory density and good color separation.

EXAMPLE XVI EXAMPLE XV EXAMPLE XV A pigment suspension is preparedconsisting of a magenta pigment, Naphthol Red B,l-(2'-methoxy-5'-nitrophenylazo 2-hydroxy-3"-nitro-3-naphthanilide, C.I. No. 12355; a yellow pigment,l-cyano-2,3-(3'-nitro)-phthaloyl-7,8-benzopyrrocoline; and as a cyanpigment, zinc phthalocyanine. This trimix is exposed to a multicolorimage and produces a full color image of satisfactory density and goodcolor separation.

EXAMPLE XVI A pigment suspension is prepared consisting of a magentapigment Bonadur Red B, l-(4-ethyl-5'-chloroazobenzene-2'- sulfonicacid)-2-hydroxy-3-naphthoic acid calcium lake; a yellow pigment,N-2-pyridyl-8,l3-dioxodinaphtho-(2,l-b;2,3 d)-furan-6-carboxamide; andas a'cyan pigment, the gamma form of metal-free phthalocyanine. Thistrimix is exposed to a multicolor image and produces a full color imageof good density and color separation.

Although specific components and proportions have been described in theabove example relating to the use of phthalocyanines in electrophoreticimaging systems, other suitable phthalocyanines, as listed above, may beused with similar results. In addition, other materials may be added tothe pigment compositions or to the pigment-carrier suspensions tosynergize, enhance or otherwise modify their properties. For example,the pigments or the suspensions may have electrical or dyesensitizersadded if desired.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon a reading of the presentdisclosure. These are intended to be included within the scope of thisinvention.

What is claimed is:

1. A photoelectrophoretic imaging suspension comprising a substantiallyinsulating carrier liquid having dispersed therein electricallyphotosensitive particles of at least two colors each of said particlescomprising an electrically photosensitive pigment said pigment beingboth the primary colorant and the primary photosensitive ingredient forthe particle, said pigment having a principal light absorption bandwhich substantially coincides with its principal photosensitiveresponse, and wherein the spectral response curve for particles of asingle color does not substantially overlap the spectral response curvefor particles of a different color, said electrically photosensitiveparticles of at least one color comprising finely divided phthalocyaninepigments.

2. The imaging suspension of claim 1 wherein said phthalocyanine is ametal-free phthalocyanine.

3. The imaging suspension of claim 1 wherein said phthalocyanine is ametal-free phthalocyanine selected from the group consisting of thealpha polymorphic form of metal-free phthalocyanine, the betapolymorphic form of metal-free phthalocyanine and the X-polymorphic formof metal-free phthalocyanine and mixtures thereof.

4. The imaging suspension of claim l wherein said phthalocyanine is ametal containing phthalocyanine.

5. The imaging suspension of claim 1 wherein said phthalocyanine is ametal containing phthalocyanine selected from the group consisting ofcopper phthalocyanine, zinc phthalocyanine and mixtures thereof.

6. The method of photoelectrophoretic imaging comprising the steps of:

a. providing a first substantially transparent electrode;

b. providing an imaging suspension comprising electricallyphotosensitive particles of more than one color dispersed in aninsulating carrier liquid each of said particles com prising anelectrically photosensitive pigment said pigment being both the primarycolorant and the primary photosensitive ingredient for the particle,said pigment i0 having a principal light absorption band whichsubstantially coincides with its principal photosensitive response, andwherein the spectral response curve for particles of a single color doesnot substantially overlap the spectral response curve for particles of adifferent color, said electrcially photosensitive particles of at leastone color comprising a finely-divided phthalocyanine pigment;

c. providing a second electrode;

d. placing said imaging suspension between said first and secondelectrodes;

e. applying a potential difference between said first and secondelectrodes across said imaging suspension; and

f. exposing said imaging suspension to a pattern of activatingelectromagnetic radiation until an image is formed.

7. The method of claim 6 wherein said phthalocyanine is a metal-freephthalocyanine.

8. The method of claim 6 wherein said phthalocyanine is a metal-freephthalocyanine selected from the group consisting of the alphapolymorphic form of metal-free phthalocyanine, the beta polymorphoricform of metal-free phthalocyanine, the X-polymorphic form of metal-freephthalocyanine and mixtures thereof.

9. The method of claim 6 wherein said phthalocyanine is a metalcontaining phthalocyanine.

10. The method of claim 6 wherein said phthalocyanine is a metalcontaining phthalocyanine selected from the group consisting of copperphthalocyanine, zinc phthalocyanine and mixtures thereof.

2. The imaging suspension of claim 1 wherein said phthalocyanine is ametal-free phthalocyanine.
 3. The imaging suspension of claim 1 whereinsaid phthalocyanine is a metal-free phthalocyanine selected from thegroup consisting of the alpha polymorphic form of metal-freephthalocyanine, the beta polymorphic form of metal-free phthalocyanineand the X-polymorphic form of metal-free phthalocyanine and mixturesthereof.
 4. The imaging suspension of claim 1 wherein saidphthalocyanine is a metal containing phthalocyanine.
 5. The imagingsuspension of claim 1 wherein said phthalocyanine is a metal containingphthalocyanine selected from the group consisting of copperphthalocyanine, zinc phthalocyanine and mixtures thereof.
 6. The methodof photoelectrophoretic imaging comprising the steps of: a. providing afirst substantially transparent electrode; b. providing an imagingsuspension comprising electrically photosensitive particles of more thanone color dispersed in an insulating carrier liquid each of saidparticles comprising an electrically photosensitive pigment said pigmentbeing both the primary colorant and the primary photosensitiveingredient for the particle, said pigment having a principal lightabsorption band which substantially coincides with its principalphotosensitive response, and wherein the spectral response curve forparticles of a single color does not substantially overlap the spectralresponse curve for particles of a different color, said electricallyphotosensitive particles of at least one color comprising afinely-divided phthalocyanine pigment; c. providing a second electrode;d. placing said imaging suspension between said first and secondelectrodes; e. applying a potential difference between said first andsecond electrodes across said imaging suspension; and f. exposing saidimaging suspension to a pattern of activating electromagnetic radiationuntil an image is formed.
 7. The method of claim 6 wherein saidphthalocyanine is a metal-free phthalocyanine.
 8. The method of claim 6wherein said phthalocyanine is a metal-free phthalocyanine selected fromthe group consisting of the alpha polymorphic form of metal-freephthalocyanine, the beta polymorphoric form of metal-freephthalocyanine, the X-polymorphic form of metal-free phthalocyanine andmixtures thereof.
 9. The method of claim 6 wherein said phthalocyanineis a metal containing phthalocyanine.
 10. The method of claim 6 whereinsaid phthalocyanine is a metal containing phthalocyanine selected fromthe group consisting of copper phthalocyanine, zinc phthalocyanine andmixtures thereof.